This invention relates to propeller driven aircraft, and more particularly to propeller location relative to the aircraft wing.
Many conventionally configured propeller aircraft have engines mounted in front of the wing. This arrangement meets structural requirements by uncoupling inertial and aerodynamic moments about the wing axis and by allowing nacelle attachment to the main wing spar. However, aerodynamic penalties result from flow interference between the wing and nacelle and from blockage of the propeller slipstream by the wing. Earlier designs have attempted to minimize these penalties by positioning the propulsion means above the wing. An early example is the Custer channelwing. In this aircraft, the wing extends outward from the fuselage to the propeller arc and then curves downward around the propeller, forming a half-circle, and then extends horizontally to the tip. More recent examples are embodied in tactical assault transports such as the YC-14 and 17 where jet engines are mounted over the wing. Each of these designs have been able to create additional lift at low speeds using induced flow over the upper surface of the wing. The additional lift is a result of increased circulation around the wing produced primarily by propulsion wash and entrained air flow over the rearward portions of the airfoil. These designs have limited application because the drag penalty is greater than conventional designs. The turbulent wake flowing over the wing reduces the laminar flow region. In addition, nacelle-wing interference may be greater with the over wing engine where nacelles and pylons extending from the wing are in an accelerated and more critical flow field. Additionally, the over wing mount tends to block a portion of the wing. The purpose of the present invention is to broaden the operating envelope of prior designs while minimizing the disadvantages thereof.
Accordingly, it is an object of the present invention to provide a propeller location which induces airflow over the wing in such a manner as to increase lift while reducing drag.
A further object of the present invention is to reduce nacelle-wing interference in order to minimize nacelle drag.
Another object of the present invention is to eliminate pylon wing interference in order to minimize pylon drag.
Still another object of the present invention is to reduce wing structural loads and particularly torsional loads inherent in many over-the-wing designs.